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What are the disadvantages of a delta wing biplane design?
The idea of a delta wing as I understand it is to reduce stress on the wing and drag on the leading edge. Now using two delta wings on separate planes, on one frame would presumably allow for a reduced wing size, and therefore less drag. I imagine it could also lead to a nice compromise with better control in slow flight than delta wing designs?
However, clearly there are some major issues with this design, as a quick search uncovers no results for this design shape. therefore I pose the question: Why is it that designers have rejected this possibility; what are its major (dis)advantages?

Welcome to av.se!  Interesting question.  You're right that designs like that don't exist, and I expect that Peter K. and others here can explain why not.  Good question!

Two wings in one plane would be a canard; a biplane has two wings in two different planes. Please describe more clearly what you have in mind!

@PeterKämpf Edited to reflect I mean specifically wings in different planes as opposed to canard designs.

Interesting question.  Well, thanks to your observation, someone now has the possibility to build the "first ever" example of a particular thing, in miniature radio-controlled form if not in full-scale manned form.

The main benefit of biplanes is that the lift can be distributed across both wings. This provides more lift with less wingspan and places less load on each wing. Less load means the materials can have lower strength. This was very important in the early days of aviation, when engine power, materials, and weight were much more limited.
The major downside of a biplane is aerodynamics. The wings interfere with each other, causing drag. While structural bracing between the wings can reduce weight, it also adds more drag. This means that a single wing will almost always perform better, and modern materials and designs should make that possible.
A biplane configuration does not make much sense for delta wings. The main drawback of a biplane is drag, but drag increases with the square of velocity, and delta wings are best in high-speed flight. While delta wings have lower wave drag, they have higher viscous drag due to the large surface area. A second delta wing will add more area, increasing both wave drag (from the cross section) and viscous drag (from the surface).
Configuration of the aircraft also becomes problematic. Most aircraft with delta wings tend to be fairly flat, allowing lower area and therefore lower drag. The closer the wings are, the more they will interfere. The further apart they are, the more structure is needed, either in a larger fuselage or in structural braces, which increases weight and drag.

Would a second delta wing add more area/drag? I would have thought that by adding a second wing it would increase the lift therefore allowing reducing the size of the wing such that these factors would cancel out

@Rugnir, biplane wings don't add linearly.  If a wing of a given area produces 1 unit of lift, then adding a second wing of the same area on top of it produces about another 0.5 unit of lift, for a total of 1.5.  This is because of the aforementioned interference.

A lot of the reason for biplanes (and triplanes) in early aircraft was strength.  You could use struts between the wings and diagonal wires to produce a strong, rigid box structure from wood and fabric.  I don't offhand know of any biplane that didn't have such bracing.  (But I'm no expert.)

Strutless biplanes are rare, but here's one.  https://en.wikipedia.org/wiki/Dornier-Zeppelin_D.I
Here's an even rarer strutless triplane (a prototype; the next version got struts added): https://www.fokker-history.com/en/de-v-serie#V-III

Lift is created by accelerating air downwards. If you use two wings stacked on top of each other to accelerate basically the same amount of air, your efficiency goes down, not up. The more air is involved in the creation of lift, the better for efficiency. Reducing wingspan will drive up the lift-dependent part of drag, because the span loading (unit of mass per unit of wingspan to carry) goes up.
Biplanes make most sense if the requirement calls for

high roll rates
minimum structural mass and
low airspeed,

which was generally why early airplane designers chose this configuration to take to the air. When engines became more powerful and the aircraft had to earn their money by transporting payloads, the monoplane won.
A delta wing makes most sense for trans- and supersonic speed. Its capability for vortex lift allows low landing speeds even with thin airfoils without powerful flaps, and its high leading edge sweep enables a subsonic leading edge even at supersonic flight speed.
It might be interesting to mention one idea for a supersonic biplane here: This could be used to avoid shockwaves, but only at one particular Mach number when the shocks of the top and bottom wing cancel each other. No airplane has ever used this concept, mostly because in order to work no lift must be created.

Besides allowing to be built of materials with less strength (which made biplanes widespread in the early days of aviation), the sole advantage of a biplane is better handling at very low speeds with a shorter wingspan. There are still some biplanes in use today, but more in the "bush plane" category, as their shorter wingspans and low stall speeds allow them to land on rough and narrow fields. The famous An-2 doesn't even has a stall speed, it lands almost like a parachute if you turn off the engine and pull back the stick. So, the main reason one would chose a modern biplane is to be able to fly it at extremely low speeds or in rough environments. Delta wings are designed for high speeds, the polar opposite of where biplanes are good at. You can't optimize an aircraft for both very low and very high speeds, as it would perform worse in both categories.

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Can the debris pattern from a crash site confirm explosion as the cause of a crash?
Is there any precedent or can the debris pattern positively confirm the cause of a crash due to:

an internal explosion OR
strike from a missile or other military projectile?

If a particular flight path is necessary to facilitate the question, assume the 1988 Airbus flight.

Removed link to recent events. We don't do accident speculation before the offical report.

Wondering why this question was tweeted?

No, not an explosion, just break-up.
The debris field can prove if some parts of the aircraft broke off in the air, before the main impact. However the aircraft can break up also if the pressure vessel fails, if intense fire compromises the structural integrity, or due to mid-air collision.
And on the other hand, an explosion can make the plane uncontrollable without breaking off any large parts e.g. if it severes the hydraulic lines (which can also start fire as the hydraulic fluid is flammable).
An explosion can only be proven by collecting pieces of the wreckage and looking for traces of spalling, shrapnel damage and traces of an explosive.

Yes, especially if the explosion or breakup occurred at altitude. In this case the pieces of the plane will be broadly distributed across the terrain and pieces with any aerodynamic qualities (big, flat chunks) will fall a significant distance from dense pieces of machinery (engines, pumps, motors).
For example, an RV-type plane flying out of an airport not far from my home crashed into an open field; one of its wings came to earth far from the crater, indicating that the wing came off not during the impact but while the plane was still in the air.
Furthermore, pieces of the shattered bubble canopy were found in a cluster far from the crater rather than inside the cockpit, where they would be if the canopy shattered on impact. This allowed the investigators to conclude that the wing spar folded at its join with the fuselage, flipped up and struck the canopy, smashing it to pieces and then separated from the fuselage while the plane was a thousand feet or so above the ground.
Explosions leave blast soot on the pieces of the plane and impact damage from pieces of shrapnel thrown by the exploding munition. A missile strike on an engine will blow it free of the wing at altitude and a bomb in the fuselage will show localized blast soot and tearing patterns in the fuselage structure which can be deduced from the wreckage with a lot of hard work.

Interesting observations, however it doesn't directly correlate. If a wing, for example, was found some distance from the rest of the wreckage, it's likely that it separated in mid-air rather that on impact - but that doesn't mean an explosion by any means.  Equally, localised soot and tearing patterns won't be visible purely from the debris pattern at the crash site - all debris would need to be collected, put together and examined.  I tend to agree more with @JanHudec's answer

Do you have any reference for the "theory" (or even just praxis) behind explosive traces analysis? Because yes, I found capillary gas chromatography should be the procedure (as pioneered by RARDE 35 years ago) but how much feasible is it? Not that I think it would be any smart for the specific missile that took down IR655 (a fragmentation warhead leaves quite more evident markers), but this crashed in the Strait of Hormuz. Even if we assume a whole ass bomb had been set off inside, how much could you still detect after a few days even in the most shallowest and calmest waters?

@mirh, sorry,  I do not know. But the NTSC people have decades of experience and specialized tools for analyzing this stuff. -NN

Yes and no. I would not use the term "confirm". When a crash is investigated all available evidence is analyzed, including the debris pattern. You would be amazed at how detailed the analysis can be. The size and shape of fragments are analyzed. The way the edges of the fragment deform is analyzed. Even the position of the edge deformities is analyzed, as this may provide a vector pointing directly toward the center of the explosive forces. From multiple such fragments triangulation can be used which can pinpoint exactly, or at least roughly, where the center of mass of the explosion was. Blast pressures at various points can be estimated, and these patterns may be consistent with some types of explosives and inconsistent with others. Chemical trace analysis of the fragment can detect traces of most explosives. Even audio from the CVR can be analyzed to help discern the type of explosion.
A laundry list of scenarios is then analyzed: is all the data consistent with a mid-air explosion; is it consistent with an engine fire leading somehow to a larger conflagration; is it consistent with an otherwise intact airplane flying in a controlled manner into terrain. This analysis produces a degree of confidence as to whether or not that scenario is consistent with the evidence. Oftentimes sophisticated statistical models are employed to quantify these probabilities. The pattern of the debris field is likely to be one such component. However, sometimes there are multiple scenarios that can well explain a certain component of the evidence. That's why all the evidence is taken together. It like a criminal investigation where a list of suspects is whittled down using each piece of evidence to exclude some suspects until finally only one suspect remains, consistent with all the evidence.
The analysis is more likely to be definitive when all of the plane can be recovered.
Of course sometimes it's pretty easy. If you find missile debris along with the plane debris, and missile fragments embedded in a section of the plane, you can probably tentatively conclude it was shot down by a missile. In a criminal investigation this would be called a "smoking gun".

Confirm, no. Give a solid preliminary estimate, yes. It has been done multiple times.
Just mapping the debris field will give preliminary answers as to the following questions:

Did the aircraft break-up in mid-air or upon impact?
At what altitude (approximately)?
Did it break up all at once, or did some part (tail, wing) break off first?
Did it collide with another large aircraft?

Every piece of debris found will be taken into evidence and analyzed. This will produce additional conclusive information:

If there was an internal explosion, it will leave buckled-out parts and exit holes in the skin. The patterns are unmistakable.
Any external explosion will similarly leave parts buckled into the aircraft and entry holes from any shrapnel.
Even a missile as small as the Stinger will leave enough pieces of its own debris to conclusively confirm its presence and type.

It takes some time to go from theories to most likely cause to conclusive proof, but generally the broad scope of the causes (missile hit, internal malfunction, CFIT, bomb on board) can be ranked into the most and the least likely ones with just the debris pattern.
Confirming anything generally means exploring and assessing every plausible hypothesis. It will usually take 1-3 years before the final report that is the only positive confirmation. That said, the most likely theory is usually established in just a couple months, and the rest of the time is spent evaluating it and looking for more alternatives.

The questions listed are appreciated.  An excellent approach to answering a vague question

an internal explosion OR

To some degree, yes.
Consider the case of Turkish Airlines Flight 981. In this case the rear cargo door blew off. It was immediately obvious what happened because they found the door, bits of the floor, and a row (or more?) of seats immediately above the door miles from the crash site. Generally, if you find some selection of parts at a distance from the rest, you can be pretty sure the problem started around there.
In the case of an internal explosion, you would expect to see portions of the fuselage or frame would be separated early. For instance, American Airlines Flight 444 led to parts of the airframe being recovered. In this case, the initial set of parts are fragmented into smaller parts, as opposed to complete parts like a cargo door. As the plane breaks up larger parts will shed, but tracking back will reveal the initial type of debris.
Alternately, you may never find those parts, leaving a clear hole in the parts inventory. This was the case for Pan Am 103, where the hole caused by the bomb could be easily seen in the reconstruction.

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Can a modern commercial passenger flight recover from failed sensor(s)?
ABC News reports a failure in a pitot tube sensor may be the cause of an AirFrance Rio to Paris flight tragedy.  Excerpts from the news include:

An Associated Press investigation at the time found that Airbus had
known since at least 2002 about problems with the type of pitots used
on the jet that crashed, but failed to replace them until after the
crash.
As a storm buffeted the plane, ice disabled the plane's pitot tubes,
blocking speed and altitude information. The autopilot disconnected.
The crew resumed manual piloting, but with erroneous navigation data.
The plane went into an aerodynamic stall, its nose pitched upward and
then it plunged into the sea on June 1, 2009.
Air France is accused of not having implemented training in the event
of icing of the pitot probes despite the risks. It has since changed
its training manuals and simulations. The company said it would
demonstrate in court “that it has not committed a criminal fault at
the origin of the accident” and plead for acquittal.

If a pilot recognizes that flight condition sensor inputs (Altitude, AOA, etc) are faulty: what prevents the pilot from "dead reckoning" and safely land the aircraft at the nearest airstrip?

That happened 13 years ago. It has been discussed quite thoroughly here: https://aviation.stackexchange.com/search?q=Af4447 Have you done any research? Is there any new development?

Additionally to AF447, there is this A330 incident where all 3 airspeed inputs failed due to forgotten pitot covers. Mentour pilot did a video on it which might be of interest to you.

@nobody That search link returns nothing. Correct link is aviation.stackexchange.com/search?q=Af447

Even the basic news report I saw recently said that this was due to pilot training and reactions, not just to a faulty sensor.

I strongly disagree that it was the failed sensor.  Failed sensors are just slightly inconvenient, but rarely a serious problem.  The real cause was the pilot's failure to respond appropriately by reading the other instruments, understanding the problem and taking appropriate action.  Also the other pilots' failure to monitor and oversee the handling of the plane.

Unfortunately not only the not-properly trained pilots but also the Human-Maschine-Interface played a role: the final Bea report contains safety recommendations also on Ergonomics.

Generally speaking: Yes it can! (no pun intended)
This is done because all critical systems are built either such that they are very, very unlikely to fail. For flight critical systems it is required that the systems fails with a probability of only 1e-9 (therefore once every 1e9 flight hours), or in other words practically never. In case of electronics this usually means that they are built redundantly, meaning two or more copies of the hardware exist such that if one fails, the other can take over. For example critical flight computers onboard the Airbus A320 or Boeing 777 which compute the control inputs for the control surfaces are redundant both in hardware and software such that one of the (two or more) flight control computers can fail without something bad happening.
A good counterexample is that of the MCAS fail in which Boeing connected only one Angle-of-Attack probe to the flight control computers. Therefore any fail in this sensor had direct consequences for the flight controls, which is exactly what happend (twice...). This resulted in the death of 346 people.
This should illustrate two things:

It vividly shows that redudancy is very much needed for the safety (btw, this is one major reason why aviation is so expensive)
Coming back to your question: Yes the pilot is able to safely return to the airstrip with one sensor fail. For more then one sensor it depends a bit on the exact combination, but in all generality it still should work.

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Why don’t large aircraft (larger than ~737-size) have even partial manual-reversion capability?
Essentially all large aircraft1 have flight control surfaces powered, either directly or indirectly, by hydraulic actuators, as do most medium-sized and some small aircraft.  Small- to medium-sized aircraft with hydraulically-actuated flight controls essentially always have some form of manual reversion capability, where the primary flight control surfaces (always the elevator and ailerons, and sometimes the rudder as well) are operated manually by the pilots, usually by control cables attached to the pilots’ yokes and pulling (depending on the aircraft) either on the control surfaces directly or on servo tabs which then generate aerodynamic forces which move the control surfaces.  This allows the flight control surfaces to remain operational in the event of a total failure of the aircraft’s hydraulic systems, albeit requiring the pilots to exert a (sometimes considerably) greater force on the controls to operate them.
Large aircraft, on the other hand, generally have no manual-reversion capability at all.  This is ostensibly due to the greater aerodynamic forces acting on their flight control surfaces at cruising speeds, which would require superhuman strength to completely overcome (despite the fact that, before hydraulic flight control boosting came into wide use, many, many large and fast aircraft were successfully flown with purely manual controls through the use of a number of force-reducing tricks).  However, in a no-hydraulics situation, having any manual control capability at all, even with a significantly- to considerably-reduced control authority and range of movement compared with hydraulically-boosted operation, would be an extremely-useful adjunct to throttle pitch control and steering (which – especially throttle steering – are difficult, sluggish, clunky, and only really usable for coarse altitude and flightpath adjustments).  So why don’t large aircraft have at least partial manual-reversion capability, despite even a little flight control authority being far, far better than nothing at all?

1 I'm using "large" here to mean "larger than a 737 MAX 10".

@757toga: 737s and DC-9-80s are not large aircraft.  767s, A330s, 747s, A380s, etc., are large aircraft.

Cables and pulleys are not without their own problems. See also Air Moorea flight 1121.

For aircraft that don't have manual control capability, the required redundancy is built into the system design with redundant hydraulic actuators powered by redundant hydraulic systems.
You can't look at it and say that some worst case is theoretically possible and you have to design for that.  The industry uses a failure analysis and risk probability approach for failures, with 4 main risk categories; Minor (not too big a deal, just extra workload - probability of 1:1000), Major (Significant increase in workload or difficulty for crew - 1:10,000), Hazardous (Someone gets hurt - 1:10,000,000), and Catastrophic (loss of the airframe) (1:1000,000,000).
So for Catastrophic events, the probability of a single component failure that causes loss of an airframe has to be better than one in a billion, and if not you have to add a backup to get it below that.  One in a billion is pretty unlikely, but not impossible, and outlier failures happen from time to time, and sometimes it's because the system safety analysis itself was flawed (that happens in a lot of cases).
What it means is that if the fully hydraulic controls are designed with sufficient damage tolerance and redundancy to keep potential failures within that risk profile, no further backup is required, and such additional equipment is effectively considered "ballast" from a design for risk perspective.
It's a cold hearted numbers game on the surface, but you have to create some kind of arbitrary mathematical model to go from or none of it would work because airplanes would have to be overdesigned to death to cater to every possible eventuality. Great fodder for trial lawyers though.

Adding in manual control mechanics for a large aircraft has serious drawbacks:

Weight: For a large aircraft, the weight of pulleys, cables, etc., will add up quickly. This costs money in fuel and by reducing the useful load of the aircraft.
Complexity: The manual system would have to be routed through the entire aircraft, including passing through pressure bulkheads and other structure. This takes a lot of time to design, install, and maintain. While there are certainly ways to deal with the high forces involved, that just adds more complexity.
Vulnerability: There have been multiple accidents in which manual control systems were improperly set up or jammed. The manual system would have to be designed so that fly-by-wire system would still work even if the manual system develops an issue. If an event is catastrophic enough to cripple all of the hydraulic/electrical systems, there's a good chance a manual system would be disabled as well.

The alternative is to design a hydraulic system that can match or exceed the reliability of a manual system. Of course this is not without its own complexities and issues, but virtually all modern airliners have gone this route. The weight and complexity of a manual system are not worth the remote probability that such a system would be both necessary and useful.

Regarding vulnerability, manual control cables still work even if there's a failure in the cables to a different control surface, whereas a hydraulic system failure will, absent special fault-isolation components in the hydraulic circuit, disable everything powered solely by that hydraulic circuit.

@Sean which is why there are multiple independent hydraulic systems, and the plane is still controllable if any two fail. Which is arguably better than a system where two failures would leave you with only one type of control left.


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What are these openings around the Comet's engine intakes?
What are all these openings surrounding the Comet 1's engine intakes...

(Original image by Tony Hisgett at flickr, via Wikimedia Commons; modified by me)
and what is this opening between the Comet 4's intakes?

(Original image by Ian Dunster at Wikimedia Commons; modified by me)

They're the chemtrail carburettor inlets.

@Sanchises You are mostly correct. The inlet between the two exhausts was for a hydrogen peroxide rocket that was never implemented.

@gwally: The pictures are of the intakes, not the exhausts.

@Sean if you look at the cutaway of mins answer below, you'll see the exhaust for the rockets. I should have taken a closer look at the second image and realized that there were lights to the right of the intake and it was the front of the wing, not the back. I appreciate the clarification.

Short answer
Top (Comet 1)
1: Air conditioning -- 2/3: Engine cooling -- 4: Likely fuel venting -- 5/6: Engine cooling
Bottom (Comet 4)
1: Engines cooling

Details
The De Havilland 106 (DH 106) "Comet" was a UK airliner, the first commercial one with jet engines, introduced in 1952 under the colors of BOAC. The last aircraft was retired in 1997. The Comet 1 is known as a great engineering achievement, but also for its initial series of catastrophic failures. These accidents led to the understanding of metal fatigue caused by decompression cycles (after a famous structural test) and the generalized use of openings with rounded corners by all airliners. Beside technical achievements, the aircraft and other of the same era are also remembered for their beautiful shapes.
Cutaway, showing how engines are buried in the wings:

Source
The Comet 1 was an interim version until the more powerful Rolls-Royce Avron engine development was complete. The Comet 1 engines were Halford H.2 Ghost aka De Havilland Ghost 50 Mk1 or simply Ghost.

De Havilland Comet 1XB - From photo by Ruairidh MacVeigh, Flickr
From left to right:

I cannot definitely identify the smaller hole near the fuselage, it might be the ram air intake used for fuel venting. A system which was used quite frequently for emergency landing until the engine bearing overheat problem had been fixed. In some description this hole is completely on the right of the outboard engine.
Ram air intake below inboard engine intake is for cabin air conditioning. Ram air goes to the heat exchanger which cools cabin air circulated in the heat exchanger. The Comet was one of the first aircraft to use bleed air from the compressor and the turbine to provide comfortable cabin pressure at high altitude.
Ram air intakes on each side of the outer engine are used for engine cooling.

On the top of the wing, there are scoops, more visible in the Comet 4 picture below.

De Havilland Comet 4 -- From photo by edk7, Flickr
The Comet 4 engines were Rolls-Royce Avon AJ.65 with twice the thrust of Halford H.2 Ghost.

The engine cooling intake between the two engines has been enlarged and the second one (outboard) removed.
The four air scoops over the wings are additional intake for engine (e.g. to ventilate fuel vapors) and accessory cooling (e.g. for alternator).

Additional information:

DH 106 Comet 1XB at Canada Aviation and Space Museum
Airliner Tech Series 07 - De Havilland Comet
De Havilland 106 Comet presentation

The rear vent between the engine exhaust was originally for a hydrogen peroxide-powered de Havilland Sprite booster rocket as a boost for the Ghost 50 Mk1 turbojet engines. Field tests indicated such a feature was not needed, especially once they upgraded to the Rolls-Royce Avon AJ.65 engines. - https://en.wikipedia.org/wiki/De_Havilland_Comet

@gwally: As @.Sean mentioned, the photos are shot from ahead, this ejector is not visible.


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Why did the Mercure fail?
The Dassault Mercure was a French regional jet that first flew in 1971 and received its type certificate in February 1974; it resembled an enlarged, shorter-range 737-200, and was designed to serve higher-capacity short-haul routes.  The Mercure was an abysmal failure, with only eleven aircraft ever sold, all to French domestic carrier Air Inter.  Wikipedia states, citing Dassault’s own website, that the killer was its short range, only 2,080 km (1,125 nmi) with a typical payload, and reducing to 1,700 km (920 nmi) at maximum capacity.
Except... that doesn’t actually explain the Mercure’s failure to sell!
Sure, it didn’t have the range for long transcontinental or transoceanic crossings, but you don’t need that much range to be successful as an airliner, as evidenced by the profits made by regional-jet manufacturers.  The Mercure’s Wikipedia article - citing Dassault - admits as much, even as it makes the claim that the aircraft was doomed by its short range:

This lack of interest was due to several factors, including the devaluation of the dollar and the oil crisis of the 1970s, but mainly because of the Mercure's operating range – suitable for domestic European operations but unable to sustain longer routes; at maximum payload, the aircraft's range was only 1,700 km.  [emphasis added]

1,700 km is plenty of range for European routes, and there are numerous other markets for high-capacity, short-range aircraft.  Japan, land of the 747 regional jet, comes immediately to mind, along with the other dense areas of East, Southeast, and South Asia and the Middle East.  Even infamously-spread-out North America should have been fertile ground, what with the multitudes of short routes (and even not-so-short ones; the Mercure would have had enough range to comfortably fly between New York and Chicago in a typical passenger configuration, although not in all-up sardine mode) in the northeastern and midwestern United States, eastern Canada, parts of the South, the West Coast, and the Caribbean.  As a point of comparison, the earlier Sud Caravelle - the fourth jetliner to enter revenue service,1 and the first-ever regional jet - had an even shorter range (1,700 km was its maximum range), and it was riotously successful, to the tune of 282 aircraft (some of the very last of these, ironically, going to Air Inter at the very same time they were contemplating the Mercure), despite also having a smaller passenger capacity.
What am I missing?  Why wasn’t the Dassault Mercure successful in the short-haul market?

1: Preceded by the Comet, the Tu-104, and the 707, in that order.

Mainly because the short haul market needed to wait for the deregulation of the late 70s into the early 80s that resulted in the creation, by the early 90s, of the hub and spoke concept with small regional jets feeding hubs where the mainliners were.
The CRJ200 was the main pioneer of this market, as an up to date rendition of a smaller regional feeder jet. At the time it was expected to sell maybe a couple hundred units, even within Canadair.

There never was a hub and spoke system in Europe, or US style deregulation.

But the US is the dominant market.  The European consumer air travel market is much smaller because there is still a lot of train travel, which is almost non-existent in NA.

which is irrelevant as the Mercure wasn't primarily targeted at the US market, but the European and former colonial French markets.

@jwenting: Actually, Dassault did try to sell an updated, CFM56-powered Mercure in the U.S., but didn't get any orders.

@JohnK: And yet the even-earlier Caravelle was a roaring success...


text:
Does a lean mixture result in a higher cylinder temperature for a given power setting?
From what I know over rich mixture help cools the engine due to evaporation process and lean mixture do the opposite.
So why this graph showing when reaching around peak EGT the opposite happens:

To oversimplify, you could say it's because when you are rich of peak you are getting temperature reduction from too much fuel.  When lean of peak you are getting temperature reduction from too much air.  Watch this guy's youtube video seminars.  They are a treasure.


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Why is the B-29 bomb bay grossly oversized?
This photo shows a B-29 filled to near capacity. By counting the 500lb bombs, we arrived at a total of 16,000lb.

Image source - B29 Wikipedia page
This looks mostly empty. It looks as if you could fit 2-3 times as many bombs.
Why is the bomb bay so oversized?
(I tried finding a similar angle of a loaded B-52, but couldn't.)

It wishes it were a Lancaster :-)

You're not counting the space between the open bomb bay doors as part of the bomb bay volume, are you?

@kwc of course I'm not

Lemme guess, been watching Masters of the air? So good.

Bigger doors allow for dropping bulky items, eg food and medical supplies, if the need arose to repurpose B-52s in desperate times.

In addition to ROIMaison's excellent, referenced answer, here's a simple, practical, common sense reason:
While there is a lot of empty space around the bombs themselves, the plane can only carry a maximum amount of bomb weight. If all that empty space were filled with bombs, racks, and all the other mechanisms to load and drop them, the B-29 would have never gotten off the ground.
If that space had been enclosed with extra sheet metal to make it precisely match the amount of space the 20,000lbs of bombs needed, it would have taken extra metal, which was in short supply in war-time, would have taken extra time to construct, and would have added to the gross empty weight of the aircraft, reducing the bomb carrying capacity.
There is simply no reason to make the bomb bay "hug" the actual space that's needed for all the bombing mechanisms. The fuselage was the size it was to accommodate everything else the plane needed to do, and leaving empty space just simply isn't an issue.
An additional up side, it probably made it much easier for maintenance crews to get into the bay to check and maintain the bomb racks. This gave them some working room instead of them having to cram themselves into a Goldilocks-like "just the right size" space.

In addition to the above, in designing the bomb bay they may have made less dense or more awkward shaped payloads in mind. The https://en.wikipedia.org/wiki/Grand_Slam_(bomb) did not properly fit in the Lancaster bomb bay, and anti personnel/incendiary weapons are probably less dense/harder to pack.

Sure is nice to have somewhere to put your other foot when you're working backwards upside down. And as an almost direct scale-up of the B17, it doesn't need to be any smaller, and with the circular cross section air frame, it doesn't need inner struts either. Began design in 1938; still had to be modified in Project Silverplate to carry nukes. It was already still too small.

@Mazura pretty sure they didn't have to expand the bomb bay to fit the nukes

Well, sort of. For the envisioned Thin Man gun-type Plutonium bomb, they needed to create a single continuous bomb bay to fit the quite long bomb. In the end, the Thin Man design was a dead end, and the Fat Man didn't need the long bomb bay. However, the Silverplate program did expand the B-29 bomb bays: See https://en.wikipedia.org/wiki/Silverplate

This cut-away image shows that there are also bombs in between the two filled columns of your image.

Image source - 39th bomb group veterans
If only 2 bombs can be stacked in the middle (due to the forward-aft crew connection tube also being located there), we arrive at a total of
(4 + 2 + 4) * 2 *2 = 40 bombs.
With 500 lbs each that amounts to 20,000 lbs, which is in alignment with the payload mentioned on Wikipedia:

Bombs:
....
20,000 lb (9,100 kg) maximum over short distances at low altitude
....

This website - Nuclear Companion confirms the 40 x 500 lbs capacity:

This cut-away confirms the 4-2-4 arrangement:

Source - Poster Depot
This image (highlighting done by me) shows a B-29 dropping bombs, and it shows 3 bombs adjacent to each other, providing more evidence of having 3 bombs side-by-side

Source - Business Insider
After some searching, I found this image, which shows bombs mounted in the middle (directly below the crew transfer tube). Even though these are not 500 lb bombs, it does confirm that bombs could be mounted in this location:

Image source - p47koji.com

It really does look like it can fit a fourth line as well

With a fourth line of bombs you would be over the payload limit.
I saw some picture of smaller bombs, they had much larger arrays, see for example this image

One aspect, that's maybe implied in other answers but not explicitly stated: flexibility.
If your bomb bay is large, it can accommodate many different configurations easily, i.e., you reach the limit of your payload in terms of weight before you run out of space.
So, why not trim down on unused space?
Different bomb configurations may/will result in different profiles of actual space occupied. Furthermore, you may want to leave room (literally and figuratively) for future expansion.
Thus, the bomb bay needs to be large enough for any known payload configurations, plus some spare room.
Thus, for any concrete payload configuration, the bomb bay will be much too large, i.e., there's plenty of unused room.

For example, fitting the first nuclear bombs in.

@ceejayoz That was my first idea as well. Ability to accommodate unconventional loads.

It's a bit like asking "why is my outlet rated 16 amps if all I ever do is plug in my nightlight and cell phone charger?"

The Short Stirling is an example of a bomb bay designed round a specific requirement. That was to carry 500lb bombs, and 2000lb armour-piercing bombs, which have similar dimensions.
Short Brothers designed a bomb bay divided into three long, narrow compartments, separated by longitudinal girders. This gave excellent strength for the weight, but meant larger bombs simply couldn't be carried: they would not fit in the space. This contributed to the rapid obsolescence of an aircraft that was excellent in many ways. Flexibility pays off in ways that you can't predict at the design stage.


text:
Could an arrow planform be better for a supersonic aircraft than a delta? Why?
From this review paper
Page 11:

Strut-bracing for the SST allows very significant reductions in both vortex and wave DDL via an extreme arrow configuration and could be favourable to LFC via reduced chord Reynolds number

All right. Low chord=low Reynolds=more laminar flow. But arrow wing=high sweep=less laminar flow.
Another paper says: Page 20:

The friction drag reduction concept is a world-first technical approach that obtains a natural laminar flow wing with a subsonic leading edge at supersonic speed. An ideal pressure distribution is first designed to delay boundary layer transition even on a highly swept wing, then an

The screen shots figures from the paper show the aircraft, an arrow-winged with a high sweep.

Here is an image found on the web.

As you can see, it has a cranked arrow wing with a nearly straight leading edge. This wouldn't even give much vortex lift, if I understand correctly.
(The aircraft shown is NEXST-1 from JAXA)
All of this is claiming that a highly swept wing can achieve laminar flow. Yet that is not what I am commonly told. So, what am I missing?

This must be a black program – your picture is a black rectangle on my screen.

@PeterKämpf it appears to be the same here, i just realized. Am trying to fix.

Now the pictures are visible and I agree with the incompatibility of high sweep and laminar flow. I was always told that the change in flow direction over the boundary layer near the leading edge of a swept wing triggers transition to turbulent flow rather soon. Maybe it is the availability of public grants which allows to maintain laminar flow in theory.

Notice how much area ruling helps.  The purple curve is warped arrow, what is the light blue?

The arrow seems to produce a little more lift.  This is consistent with a longer leading edge creating a stronger vortex.  The Concorde prototype was a nose to tail "slender" delta, not unlike a common paper airplane.  They may have gone with the ogee to mitigate the tornado-like vortexes (enough not to destroy every airborne object nearby), or noise abatement.  Would like to see slender delta data there too.  Laminar flow across that type of wing seems laughable.

60% laminar flow with subsonic leading edge(!)

@RobertDiGiovanni I thought the vortex needed to be directed over the outboard wing, and this could only be done by sweeping the outboard wing less.

Seems the ogee was selected to improve pitch control.  But improvements in this design for a 21st century SST would certainly be welcome.  It is noted that "cutting out" the rear portion of the delta and placing a smaller horizontal tail area further back may reduce drag, but is re-creating a swept wing design, with its issues.  Concorde builders may have decided what they had was good enough.

Yes, sweeping the outboard wing less is present in the "ogee" too, the remainder of the span is then "clipped",  Lift/Drag comparisons are interesting here.  Some designs have variable sweep for the outer wing only.  Getting both high and low speed performance was difficult for this design.  Their solution was to use very high AOA vortexes for low speed lift, hence the drooped nose.

The NLF is shown as having reduced drag even more than area ruling. Also, what the heck is "warped arrow effect"?

The first thing to note is that these papers are from 2003 and 2013 respectively. Since then, they have not set the world on fire.
One concern over their quality arises when I recall that the "Warped NFL wing" is typical of the reflex-cambered supercritical wings first developed around the 1970s. If you check out the inner section of say the Airbus A380 (and I suspect any modern jetliner) you will see a certain amount of that technology incorporated. But laminar flow notoriously vanishes once you fly into a few bugs or some mechanic leaves an oily smear and, despite being touted back then and as far back as the late 1930s, it has only ever produced modest results on any flyable airplane.
Next, what about this braced wing concept. The linked source discusses it on Page 10:

"A possibly viable alternative configuration for the
conventionally sized long-haul CTOL transport mission is the strut-braced wing. Strut-bracing allows
thinner, smaller chord, lower sweep and higher aspect
ratio wings. The smaller chord, leading edge radius
and sweep have a favourable influence upon HLFC,
increasing the amount of wetted area laminarized and
reducing suction mass  ̄ow and roughness sensitivity as
well as increasing attachment line stability. Other
`strut-related’ benefits include large drag due to lift
reductions from the wing tip engines and greater span
enabled by the strut, as well as large wing weight
reductions. Circulation control, powered by the auxiliary power unit, could be utilized on a conventionally
sized tail to work the engine-out problem. All these
benefits produce very large increases in the lift±drag
ratio and range at cruise."

It also notes on Page 5 that:
"More unconventional supersonic applications of [laminar flow control], again by Dr Pfenninger, to a strut-braced high aspect ratio arrow wing configuration indicates phenomenal performance levels, L/D on the order of 15-20 versus the 9-11 typical of advanced conventional configurations (with LFC)."
Now I don't know about you, but when I read of a "phenomenal" 40% drag reduction sought 17 years ago but never realized, I smell a rat. I wonder what software modelling the researchers used - 2D or 3D? At sharp sweep angles it totally matters. Were they naive enough to assume flawless laminar surfaces maintained throughout a transcontinental flight? And engines at the tips of the wings, evidently in a kind of sesquiplane variant of the Busemann biplane? Oh, spare us the FAA's demand for directional stability combined with altitude maintenance and adequate range in the mid-Atlantic one-engine-out condition.
So I think you can see where this is going.

Engines at the tips of the wings? It sounds like you misread it. nclude large drag due to lift reductions from the wing tip engines This is meant to show how placing the engines at the tips of a low AR, cantilever wing is bad, and not doing so on a strut-braced wing is good.

gliders use bug wipers....?

https://aviation.stackexchange.com/questions/78471/how-high-does-the-bug-layer-extend/78535#78535

@Abdullah, I think maybe "Other `strut-related’ benefits include large drag due to lift reductions from the wing tip engines and greater span enabled by the strut" is defeating your reading skills rather than mine.
Do gliders have bug wipers over the whole wing surface? No, I didn't think so,
You really don't need many bug encounters to screw over a scheduled commercial service.

Other `strut-related’ benefits include large drag due to lift reductions from the wing tip engines and greater span enabled by the strut notice the quotes around 'strut-related'. And if you look in the whole paper, you will see only one strut-braced concept, and that will not have it's engines anywhere near the tips. And why would they consider drag and loss of lift a benefit? Though I do think they could have been more clear.

@Abdullah; perhaps you and I are reading "strut-related benefits include large drag due to lift reductions from the wing tip engines" in very different ways. To me it is implying that the design has both struts and tip-mounted engines. But it is a convoluted presentation, following it needs fine attention to grammar and syntax. It would be clearer if expressed as, "strut-related benefits include large drag-due -to-lift reductions via the use of wing tip engines."

drag is not a benefit

That is where you are being misled by the convoluted syntax of the sentence. He is actually saying that the benefit is the reduction in drag-due-to-lift.

You're reading reduction of lift-induced drag while I'm reading drag increase due to lift reduction.

If he is saying what you think he is, then he's basically saying an advantage of struts is that wingtip engines reduce drag which doesn't make sense because a strut has nothing to do with wingtip engines.

Well, if he is saying what you think he is, you do not tire of pointing out that that makes no sense either. Which nonsense is it to be? Perhaps there is a third reading which does make sense. Take my word for it, I am familiar with these kinds of verbal convolutions in English, German and Latin, from the most technical of prose to impressionistic poetry. To me it is perfectly clear what he means. But of course, you are welcome to your own view.

meow i'm not putting engines on the wing

TBH I don't know now whether to accept what you're saying or find it strange that he linked strut bracing with wingtip engines.

I do find it strange. But I would have to see his original paper to know more.


text:
How does latitude affect the air temperature at 8 km altitude where planes fly?
Is the air temperature (at 8km) above the North or South poles colder than the same altitude above the equator?  Why?
Ground level air temperature difference between coldest and warmest places on Earth can be >70C. As you get higher, the temperature drops, of course. Does it mean that near Arctic circle air temperature at let's say, 8km altitude still maintains approximately the same difference with the 8km altitude above equator as at the ground level? Or does it even out? Is it perhaps even possible to have air at some altitude significantly warmer than at ground level?

The temperature decreases at approximately 3.57 degree Fahrenheit per 1000', the adiabatic lapse rate, until hitting the tropopause, the boundary between the troposphere (lower altitudes) and the stratosphere. At that point the temps flatten out. The lapse rate is pretty constant everywhere, so yes, it should be colder at higher latitudes for the same altitude.
But...
The tropopause is at a higher altitude at lower latitudes, so you actually end up with cooler temps above the equator then above the poles for very high altitudes (17 km range).

In the troposphere, air at altitude is colder than air at ground level. But surprisingly, air at altitude at the poles can be warmer than air at altitude at the equator. From the wiki article on troposphere (I added the bullet points):

The troposphere is heated from below by latent heat, longwave radiation, and sensible heat. Surplus heating and vertical expansion of the troposphere occurs in the tropics.

At middle latitudes, tropospheric temperatures decrease from an average of 15 °C (59-degree Fahrenheit) at sea level to about −55 °C (-67-degree Fahrenheit) at the tropopause.
At the poles, tropospheric temperature only decreases from an average of 0 °C (32-degree Fahrenheit) at sea level to about −45 °C (-49-degree Fahrenheit) at the tropopause.
At the equator, tropospheric temperatures decrease from an average of 20 °C (68-degree Fahrenheit) at sea level to about −70 to −75 °C (-94 to -103-degree Fahrenheit) at the tropopause.

The troposphere is thinner at the poles and thicker at the equator. The average thickness of the tropical troposphere is roughly 7 kilometers greater than the average tropospheric thickness at the poles.

There is quite a bit of variation in the troposphere as a function of place on earth, and much effort has been put into creating a standardised atmosphere that can be used for practical purposes around the world. The ICAO standard atmosphere serves that purpose. It cannot account for local wind conditions and humidity.

I found a graph in an old paper format uni book on the atmosphere, depicting average conditions in two separate places on earth, Berlin and 40° latitude in North America. The graph shows that although the temperature lapse rate is very similar in both cases, there is a difference in temperature at a given height. The arrow gives the temperature difference at 8 km height, also transported to 0 m (less average difference) and to 10 km (more average difference).
Above is for average temperature at two different places on earth, at similar latitudes. I could not find any direct comparison between average temperature at altitude of the poles and the equator - the wiki article seems to indicate that average temperature at the poles is higher at high altitude, a surprising indicat

I recently flew over Greenland, at cruise alt temperature was −66 °C. So there are significant deviations from (any) model of the atmosphere.

Note that the wiki article is quoting temperature in the troposphere.  It also says that the tropopause (top of the troposphere) is much higher near the equator than at the poles.  Reading further, it turns out that the tropopause is at 9km at the poles, and 17km at the equator.  It's not surprising that air at 17km is a tad cooler than air at 9km.  I'd expect air at 9km at the equator to be warmer than air at 9km at the poles.

In fairness, I'd call −45 °C 'less cold' rather than 'warmer' than −70...−75 °C. When you say 'warmer than the equator', it conjures up penguins in Bermuda shorts.

@MartinBonnersupportsMonica: May be interesting: The Tropopause in the Polar Regions. (for those who don't know yet: Who's Monica)

The airplanes do not cruise at a certain altitude, but at a certain pressure level. That could be an irrelevant nitpick if the temperature did not directly affect the pressure as a function of altitude. But it does (through the hydrostatic equilibrium). In colder areas the air is heavier and flight levels are lower as can be seen in maps of geopotential height
At FL360 the pressure is 225 hPa and the altitude is around 36 thousand feet. The 300 hPa and 250 hPa will be quite typical flight levels for airliners (~FL300 and FL340). You can see the current map of altitudes and temperatures for these and other levels at http://weather.uwyo.edu/upperair/uamap.shtml
For example: http://weather.uwyo.edu/cgi-bin/uamap?REGION=nh&OUTPUT=gif&TYPE=an&LEVEL=300&date=2020-01-09&hour=0

The green numbers are temperatures, the blue numbers are altitudes. You can see that for the same flight level the aircraft is at 9600 m above North Africa or Florida and at 8400 m near the north pole in the current weather. In summer the air is warmer and the flight levels are higher as you can easily see by choosing a different date in the app. Also, the south-north gradient is weaker in summer - related to the strength of the polar vortex.

Due to the air compressibility you can never have higher temperatures in the stratosphere than at the Earth surface. However, in certain sense, the air at higher levels IS actually warmer. The potential temperature is higher and if the air is brought to the surface pressure level, it will be indeed warmer. However, that costs mechanical energy (work).

In stratosphere, even the actual temperature increases with altitude. However most aircraft only barely reach stratosphere, or not at all when it's warm and the tropopause is high.

@JanHudec Of course it does and temperature inversions are not uncommon in troposphere either. But it certainly does not reach the surface temperatures of standard atmosphere. Not until the thermosphere. Perhaps it does reach surface temperatures of cold regions, but that is at the boundary with mesosphere where the air is very thin. That is almost space, rather than flying altitude. WAY above SR71 capabilities.

authors: Vladimir F Героям слава


text:
How many AOA sensors does the 737 MAX have?
How many AOA sensors does the 737 MAX have?
Given that it's reported in the media, that one faulty AOA probe activated the MCAS on the Lion Air flight, I was wondering if anybody also knows how an input consensus is reached for the AOA value that gets send to the MCAS system.

you have two different questions there. would you like to know how many sensors are there, or how consensus is reached?

https://aviation.stackexchange.com/questions/57626/which-737-generations-doesnt-have-alpha-vane-angle-of-attack-sensor/57634#comment150605_57626 looks relevant.

@aCVn meh, unsourced

@Federico Indeed, but still a starting point. And there's the recent news that Boeing is changing some piece of flight software in response to the recent crash. (Sorry, I haven't dug into that further.)

@aCVn https://chat.stackexchange.com/transcript/message/49433516#49433516

@aCVn the answer you posted also only says that the 737 does have an aoa probe and what it´s used for but not how many or how they interact

@hph304j that's not an answer, it is a comment, and thus you should treat it with skepticism

The Boeing 737 MAX has 2 AoA sensors.
However, MCAS only takes input from 1 AoA sensor at a time.

Sources:
The black box flight recorder data for Lion Air JT610 shows the data from 2 AoA sensors, labeled "Left" and "Right".
Also, if you look at the nose of the 737 MAX, you will see a left and right AoA vane. (The sensors with the red tags are pitot tubes).
"[Boeing] said it will change the MCAS software to give the system input from more than one AOA sensor."

Thanks @mike, do you happen to know the manufacturer of the AoA vane on 737 max?

I really enjoy this answer. Concise and documented.


text:
What happened to this airplane at Lombok Airport?
Last month I was in Indonesia and I had to take a flight from Lombok International Airport (IATA: LOP). While I was waiting for boarding I noticed an airplane (wreck) next to the runway that was somewhat burned down at the front (fire?).

The abandoned plane at Lombok International Airport. (personal photo)
I was intrigued by the way that it was just placed there, so close to the runway. I thought about an accident where this aircraft was involved in, could've have just happened a couple of days or weeks before. But I couldn't find any source in collaboration with this particular airport. I maybe thought that the airplane was used to train fire fighters, as I see that more often on other airports in the world. I tried to find more info about it on the web, but no luck.

The airplane on the map
I also headed out to Google Maps, Bing Maps and Apple Maps to see if the plane was there.
Google Maps has the airplane on its map (see image below, top middle and slightly to the left), the data is from 2016, so says the footer.
Google Maps location of airplane on Lombok International Airport, data consulted on 2 Dec 2016.

Bing Maps isn't having the airplane on its map, but maybe that's because the map is outdated (?).
Bing Maps location of Lombok International Airport, data consulted on 2 Dec 2016.

Apple Maps shows an airplane in almost the same spot (it's just on the concrete I think), but is it the airplane?
Apple Maps location of 'airplane' on Lombok International Airport, data consulted on 2 Dec 2016.

Zoomed pictures of the plane
The above picture is zoomed in on in the following pictures. Unfortunately, the aircraft registration is not visible.

And now?
I'm eager to know what happened to this plane. What type is it? Who is the owner? Can anyone tell me? Thanks in advance.

It is entirely possible that it is there for firefighter training.
It may be an old, decommissioned plane that they can start small fires in, and plan how to approach a plane, practice aiming their water cannons and putting the fires out.
I believe that is the purpose of this plane, at Seattle's Boeing Field.

It used to be an exhibit at the Museum of Flight before being replaced, and was evidently removed recently. Seems like it was just being stored, doesn't seem to be a lot of evidence of traffic to it.

It would be unusual to store other planes near the plane used for firefighter training. Also, there doesn't seem to be much damage to it.

They don't actually set a plane on "blazing-fireball inferno" for training.  They can use a lot of smoke, and some relatively low-temperature combustibles to simulate a big fire and practice approaches and techniques.

That plane was not used for fire training at BFI. I don't know its purpose, but there is a different area closer to the fire station that has some fire training equipment. The one in the sat photo has no smoke damage on it.

@abelenky that entirely depends on the level of training.

I know this is an old question, but as I ran into it, might as well comment: evac training with smoke: possible, fire training even with "small" fires, not likely, playing with fire iside an aluminium tube is not recommended

Aircraft was not there anymore last September. Probably scrapped. Photo taken in 2017.

Thanks Alex for your update! I think this is more a comment to the question.


text:
How much hand-flying does a commercial pilot do?
What is the ratio of hand-flying to autopilot for a typical commercial pilot working for a large airline (British Airways, Virgin, EasyJet etc.) and how many hours a year might a typical captain rack up for hand-flying (on the job)?
This question came to mind after reading an ex-pilots rant here on Quora. Here is an excerpt:

Back in my day (yawn, boring old f . . . fellow alert) we spent years as a co-pilot before getting a command. Now it seems, 4,000 hours is all that’s needed, often a lot less. It wouldn’t be so bad if the pilot in question actually flew the darn machine, but for much of the time they are required to use the autopilot. Just no fun.
So, maybe five years from flying tiddlers at flying school to stepping into the left seat and nervously taxiing out for that first takeoff. Ahhh, not enough to be a good cyclist, let alone be in charge of a machine that gobbles EDIT a tonne of air a SECOND into each engine during the cruise and gulps fuel by the tonne.
Other skills? The sky may look empty, but you are very much NOT alone. I’ve had nights when I couldn’t get a word in edgeways and had to ‘hold’ in some arbitrary place until I could carry on to the landing just because of not being able to liaise with ATC. Trying.
Another skill? buying enough go-juice to get to where you’re going - with a very specific bit to spare. OKAY, HERE’S A TOUGH ONE.
You have low hours. A bullying boss. Carrying fuel costs money so you want minimum - or so they tell you. NO! The skill of telling bullies where to shove their low fuel suggestions is an important one - if you don’t want tea and bikkies with you boss followed by you tax and insurance forms. I’m having the fuel I want, and here’s why! You can say that when you’ve got a bit of experience under your belt.

And as an 'off the record' question... would it be inappropriate for me to ask the CC how many years / flying hours the captain has under the type we are flying in when boarding?

Personally I wouldn't read too much into that rant - it's pretty typical of an older (in this instance retired) industry person bemoaning the newbies. Everyone tends to perceive it was harder for them to do [x, y, z] when they started in an industry. I'm sure people who flew in the 30's and 40's and 50's in things like DC-3's thought people like the above were just playing at it too. I mean, c'mon, where's your tailwheel and engine management! And yes, I think that question would inappropiate and unlikely to be answered

@Cloud you think way, way too hard about this stuff.  You've gotta learn to relax and look at the statistical probability of getting killed in an airliner flown by western crews - too microscopic to bother with, compared to the ride to the airport in a cab (which should be the really terrifying part).  Non-western crews?  A bit higher, to do with certain cultural issues like old fashioned attitudes to command, and which the industry is working on, but still very very low.

@JohnK Thanks for the comment, I appreciate it - but still not sure the question deserves a downvote - it is a viable, on-topic question with a relatively quantifiable answer.

@Cloud The downvote may be due to the rant copied verbatim, which has no bearing to the actual question. (I did not downvote, but it's a duplicate nonetheless)

Cloud, I completely agree with you that the question does not deserve a downvote, but your addendum in the comments is basically like shooting yourself in the foot, since you know that such kind of comments will set readers against you. It would be much better if next time you would keep the things completely separate and, if you really want to ask what you have now in the comment, just ask it in chat

That depends on the commercial pilot you’re talking about.  Airbus drivers are probably operating the aircraft with the autopilot engaged over 90% of the time, an ag app guy will fly manually 100% of the time.

@Cloud I didn't apply a downvote and your question is actually a very good one because there is a debate on this going on in the industry.  I reacted to your follow on comment/question that revealed maybe a bit of an obsessive over-concern on safety.  Try to get a handle on it.  I hope the stuff you learn on here helps with that.

Also related: this, this, this

An airline pilot flying a jet probably won't do much hand flying.  This is not because they're lazy, it's that airlinrs tend to have operation specifications (opspecs) that may require use of the autopilot above certain altitudes.  In this case, the pilots cannot hand fly.
Small commercial planes (Beech 1900, Metro, etc) may not even be equipped with autopilots.  Planes in passenger service tend to have them installed moreso than their cargo carrying counterparts but, still, it's hit and miss.
Small planes (Piper Navajo, Twin Cessnas, etc) that fly commercially rarely have functioning autopilots so the pilots must hand fly.
So, to your question, pilots of large jets don't do much hand flying for the amount of time they are in the air compared to pilots doing other kinds of flying or flying smaller planes.

The biggest surprise for me when I got a jet type rating was that, provided you were able to adapt from something slower to the space/time environment of a jet, they are very easy airplanes to fly and take less actual physical skill to land than a typical single engine taildragger.  The demands are mostly mental and workload related.

@JohnK So an A320 is easier to land than a Cessna? That is surprising to hear (not sarcastic)

I've flown about 25 different models of light aircraft and gliders, taildraggers, floats, and the CRJ series of jets.  The CRJ200 was one of the easiest to land.

@Cloud Most common Cessna's are not taildraggers. You've extrapolated a comment inaccurately.


text:
Who has the higher authority, the pilot in command or ATC?
I'm sure many people have heard about the communication between a Delta flight 2244 and Atlanta tower being on news today.
When the Controller informs the Pilot he is on a wrong taxi-way, things get a little heated up.
Regardless of who was right who was wrong, there were many lives involved (i'm sure they were not put in danger) but then who takes precedence in such a situation?
Can the controller tell the aircraft to stop dead in its tracks or turn back to the hangar for violating his instructions because there are other planes coming in to land and this can become a little dangerous?
Note: I am fully aware that no one was close to danger and lives were not at risk, but still pilot did worry that there is another plane coming down.
Was the pilot right in saying

We'll taxi out there any way we want when you tell us to.

For those who missed. Here is the whole story
Note
Please note that this reporting on that article is misleading. It is about taxi clearance and not landing on a wrong runway, However I have no control of what reporters write in their articles. The transcript itself is clear.
Hear the original ATC audio here

Re "Was the pilot right in saying 'We'll taxi out there any way we want when you tell us to'" -- of course he was not right.  If he feels he need to turn off his engines and vegetate indefinitely, in the interest of safety, that's fine, but he is certainly not entitled to "taxi out any way he (we) want(s)."

It isn't a black and white issue of who has higher authority.  A pilot in command (PIC) is the ultimate authority for the safe operation of his airplane.  An air traffic controller is the authority for the block of airspace or pavement he controls.
When you are operating under ATC, it is your responsibility to comply with their instructions as long as they fall within the regulations, they are safe and you are able to comply,  If ATC issues an instruction contrary to regulation or something that would compromise safety, that is when you exercise your PIC authority to deviate from their instruction.  If you are unable to comply, you exercise your authority to deviate and explain why you are deviating.  When you cannot comply with an ATC instruction, for whatever reason, it is the job of ATC to accommodate your and move other airplanes out of your way.
The regulatory basis for the PIC authority and ability to deviate from ATC instructions is in 14 CFR 91.3

§91.3   Responsibility and authority of the pilot in command.
(a) The pilot in command of an aircraft is directly responsible for, and is the final authority as to, the operation of that aircraft.
(b) In an in-flight emergency requiring immediate action, the pilot in command may deviate from any rule of this part to the extent required to meet that emergency.
(c) Each pilot in command who deviates from a rule under paragraph (b) of this section shall, upon the request of the Administrator, send a written report of that deviation to the Administrator.

The basis for ATC's authority is 14 CFR 91.123

§91.123   Compliance with ATC clearances and instructions.
(a) When an ATC clearance has been obtained, no pilot in command may deviate from that clearance unless an amended clearance is obtained, an emergency exists, or the deviation is in response to a traffic alert and collision avoidance system resolution advisory. However, except in Class A airspace, a pilot may cancel an IFR flight plan if the operation is being conducted in VFR weather conditions. When a pilot is uncertain of an ATC clearance, that pilot shall immediately request clarification from ATC.
(b) Except in an emergency, no person may operate an aircraft contrary to an ATC instruction in an area in which air traffic control is exercised.
(c) Each pilot in command who, in an emergency, or in response to a traffic alert and collision avoidance system resolution advisory, deviates from an ATC clearance or instruction shall notify ATC of that deviation as soon as possible.
(d) Each pilot in command who (though not deviating from a rule of this subpart) is given priority by ATC in an emergency, shall submit a detailed report of that emergency within 48 hours to the manager of that ATC facility, if requested by ATC.
(e) Unless otherwise authorized by ATC, no person operating an aircraft may operate that aircraft according to any clearance or instruction that has been issued to the pilot of another aircraft for radar air traffic control purposes.

Absent an emergency, an urgent need* or an inability to comply with ATC, a pilot is required to obey an ATC clearance.  Given this relationship and its exceptions, its is hard to quantify who has a "higher" authority.  Both are the ultimate authorities of their domains, but who overrules who is dependent on the situation.  In general however, ATC will be issuing proper clearances that a pilot is bound by regulation to follow, though the pilot must exercise his authority to execute that instruction in a safe manner.
*Urgent needs include things like TCAS RA events and things like weather deviations.  In most cases ATC will help you out with a deviation, but if a controller refuses to allow a deviation, I would happily exercise my PIC authority to safely operate my airplane and turn left/right a few degrees rather than penetrate a thunderstorm updraft.

In the particular case above, the audio exchange between DL2422 and Atlanta ground is

DL2422: Good morning Atlanta ground, delta 2422 approaching 3 South taxi Quebec

DL2422 is at the southern exit of ramp 3 and requesting taxi with ATIS information Q.

Ground: Delta 2422, behind the MD88 from your right, runway 27R, taxi via Mike and hold short of Dixie.

ATC has instructed DL2422 to let an MD88 pass from right to left, to taxi on taxiway M to runway 27R but to hold short for taxiway D (in ATL D is "Dixie" due to the larger number of "Delta" airplanes).  To follow this instruction, an airplane should taxi south from spot 3S on taxiway L5, cross L and then turn left on M, then taxi on M, stopping short of D and awaiting further instruction.

DL2422: OK behind the 88 from the right, 27R Mike short of Dixie, DL2422

Here, DL2422 acknowledges this correctly.

Ground: DL2422 they won't let you go to Charlotte until 57 minutes after the hour, time now 29 after
DL2422: OK copy 57, DL2422

DL2422 has been issued a wheels-up time, but their taxi clearance has not been amended.  They are still cleared to taxi via M short of D.  Sequencing to meet this time will happen east of D in further clearances.

Ground: DL2422, you are supposed to be on M
DL2422: Yes sir, we're going out there right now.
Ground: Looks like you joined L
DL2422: You know what, we'll taxi out there any way we want unless you tell us to, I don't like your attitude.
Ground: I don't have an attitude sir, I'm just saying it looks like you joined L instead of M and I'm just trying to correct you before you stay on L.
DL2422: Ok, cause my god, there's another plane out there, its like 6 miles away.  Your attitude is really something sir, we're out here on M. Good morning.
Ground: Good morning.  There was no attitude, I was just trying to correct you, that's my job to correct you if you mess up.  I'm just trying to make sure everyone is doing what I ask them for certain reasons.
DL2422: You make a mistake every 2-3 minutes, but my attitude is not like yours, we're out on M and you didn't tell us how to get there so next time you can try doing that.

The DL captain is making a scene and a very roundabout argument that the taxi route did not specify how he was supposed to transition from spot 3S to taxiway M.  I agree that this is the case, but do not understand why any assumption would be made other than to taxi straight out and turn left on M.
This is a good example of a minor deviation that had DL2422 just turned right and then left and said "oops, fixing that, joining M, thanks!", then that would have been the end of it.  This captain's unprofessional display will instead net him disciplinary action and classify his deviation as "willful" rather than "accidental".
For a clearer visualization of the event, see this image:

In this image, the green circle is the starting point of DL2422 and the blue line is the cleared taxi route with the assumed transition to M via L5.  The short red line is the initial taxi route DL2422 took.  It is not clear where they transitioned to M, so I did not extend the red route past the first possible transition.

There appears to be some controversy over the verbiage of "behind" used in the ATC taxi clearance.  The only reference I can find to this word in a cursory search is in FAA order 7110.65 (ATC procedures) in section 3-7-2 that gives example taxi clearances.  This does not define "behind" but does give distinct examples that clearly differentiate "behind" from "follow".  Given that I cannot find a better reference, all I can offer instead is years of experience in a 121 cockpit based at busy airports like IAH and EWR and plenty of visits to others like ORD, ATL, LAX, DTW, IAD, etc where clearances involving the words "behind" and "follow" are quite common.

Behind Use of this word means that you are waiting for an aircraft to pass.  You are giving right of way or yielding to the traffic in question.  This clearance is often given when holding short of an intersection and waiting for perpendicular traffic to cross the intersection before you continue through it.  Much like waiting at a stop sign in a car.  You are not expected to follow the airplane in question and even if you are assigned a turn to taxi along the same route as the airplane, you have your own clearance and are not following that aircraft.
Examples:

"Continental 1234 taxi to runway 22R at W via K hold short of S", followed by "Continental 1234 you'll see a B767 passing right to left on S, behind him continue to runway 22R at W via K R hold short of W"

In this case it is quite explicit that an airplane will be passing across your route of taxi and after it passes you are to continue taxiing straight ahead -- not to follow that airplane.  Consider an alternate setup:

"Continental 1234 taxi to runway 22R at W via K hold short of S", followed by "Continental 1234 you'll see a Citation from the right at S, behind him taxi via S W hold short of R.

In this case, you are waiting for traffic from the right again, but this time you are turning left after it passes.  You will be taxiing behind it, but you are not following it.  The Citation has a clearance to taxi S, cross runway 29, to parking.  Your clearance is S turn right on W -- to follow the Citation would be wrong.
Follow Use of this word means you are going to fall in behind this airplane and follow it wherever it goes.  You clearance is no longer a specific taxi route, but simply to follow the airplane.
Examples:

"Jetlink 1234, your sequence is the third airbus to your right, the one painted purple.  Follow that airplane to runway 22R at W.  Once behind him, monitor tower, you are number 28 for departure.", which will be followed by
"United 3412, hold short of J, let the EMB-145 get in line then follow him to runway 22R at W.  Monitor tower passing L, you are number 29 for departure"

These clearances are used to get airplanes in line in a specific sequence and simplify giving repeated complex taxi instructions when you can just follow to conga line to the runway.

Was there any implication that DL2422 was supposed to follow the MD88? Perhaps there was some miscommunication.

There shouldn't be any miscommunication there.  That kind of sequencing is common at the busy airports.  If the intent was to follow and not just wait, that word would have been specifically used.

What does the phrase "behind the MD88 from the right" mean? If it means after the MD88 passes you from right to left, then do what you want to get to where we told you. Or if it means (follow) behind the MD88, passing you from right to left. Perhaps ATC was not AS clear as they could have, or maybe, should have been. Please note, I completely agree that the Captain should have just 'manned up' and agreed that he incorrectly entered L, and asked ATC for correction guidance.

@CGCampbell it means "Pass behind the MD88 (airplane) approaching from your right".  In other words, wait for him to go by before you start taxiing.

"When you cannot comply with an ATC instruction, for whatever reason, it is the job of ATC to accommodate your and move other airplanes out of your way."
Or they might just move you out of the way, instead, as the case may be (except, of course, in the case of an emergency.) If, for instance, a plane were unable to hold the assigned speed for an approach, they might be sent around rather than sending another plane around. The controller will accommodate your inability to follow the initial instruction, but it might be you that goes around rather than someone else, except in an emergency.

@Articuno Because the instruction to follow would be declared as such: "Give way to MD88 from right to left and follow mentioned traffic". Behind is used as another phrase for "give way to". Compare to conditional clearances:
"DLH123, behind landing company Boeing 737 on 3 miles final, runway 23L, line-up and wait behind". There is no implication to follow the traffic.

Unfortunately nothing explicit, the only source I have is the German NfL, which has all three phrases within a different context:  NUMBER (figures) FOLLOW (type of aircraft) (position) MAINTAIN OWN
SEPARATION, BEHIND LANDING / DEPART-
ING (traffic information) LINE
UP RUNWAY (designator)
AND WAIT BEHIND and * GIVE WAY TO (description and
position of traffic)*.
I understand where you see the ambiguity. My trigger to follow another traffic would be if the instruction follow is actuallyused in the clearance. I have no other reference, unfortunately.

@Articuno Just to add this: The instruction to follow another traffic and additionally giving a complete taxi instruction with taxiways would be contradictory and would ultimately challenged by the aircraft crew and asked for verification. When behind is understood as give way, there is no contradiction between having traffic pointed out and then being asked to follow a taxi instruction.

@Articuno Woo, I am convincing! :) I am not sure on FAA phraseology, so maybe someone can look into the proper references if give way is even used in the FAA phraseo. I can definitely point it out in my German NfL and AIP.

The professional way for ground to handle it would have been to give taxi instructions from the current position when the discrepancy was noticed. Assuming intermediate taxi instruction was given earlier the pilot knows he took a wrong turn; ground knows he took a wrong turn; ground knows that the pilot knows he took a wrong turn. What ATC said was a dig - that's how I would have taken it. ATC started it and there's no time for that crap in the middle of "the push" at Atlanta of all places. OMG. How the pilot responded was an embarrassment to every flight crew on frequency.

@Articuno I have added some text to the answer addressing "behind" vs "follow".  Its hard to dig up a citation for this, but these are commonly used at busy airports and anyone operating there should be familiar.

@reirab I agree with your example with the approach aircraft not complying with a speed restriction being sent around, but if he goes around that itself is complying with ATC.  If he further chooses to deviate (e.g. continue to the approach) whether he declares and emergency or not, ATC still has to maintain separation and will achieve that by moving other airplanes out of the way.  Granted, the deviant pilot is going to have to answer for his behavior, but ATC isn't going to purposefully compromise separation just because someone goes rogue.

@casey Yeah, you're right there. I just meant that the controller is still supposed to have the say over who does what in that situation. But, you're right, if a pilot starts disregarding ATC instructions, the controller will keep other aircraft clear of him (and the deviant pilot will likely be having a less-than-friendly conversation with an FAA employee after he lands.)

I agree with radarbob, the controller started it and did not give the right instructions. The DL PIC was pretty rude, but basically he was correct. Also, if you listen the PIC says "ROUTE ON MIKE", demanding a re-route which he had every right to do, so your allegation that he would be disciplined is just not true, since he was going by the book and the controller was screwing up.

If L5 is controlled, then controller should have said "Behind the Md80 from your right, taxi to 27R via Lima5, Mike, hold short of Dixie..." if L5 is not controlled the captain can taxi to Mike any damn way he feels.

The general rule is: "The pilot in command is ultimately responsible for the flight and its safety". So if the pilot decided it's better for him to use a certain taxiway due to weight/wingspan or he cannot land on a certain runway, he can make ATC aware and they will try to accommodate.
Pilots are expected to follow instructions and clearances of air traffic control under normal operations, unless this would pose a threat to aircraft security or is simply not feasible.
The ATC has the possibility to instruct an aircraft on ground to stop immediately or at the next intersection, etc.

"DAL123, hold position"
  "DAL123, hold short of Alpha"

If the pilot is unable to comply for whatever reason, he must make the air traffic controller aware of this:

"DAL123, unable"

ATC has no way of forcing someone to return to the gate, if the pilot does not follow the instructions to return. They could even take off without clearance, but rest assured that they would be met upon arrival at their destination and an investigation opened into why they did not follow instructions. This is also true for using a wrong taxiway, the pilot will be asked to stop and rerouted via the correct taxiways. Mistakes happen, but when instructed to follow a certain set of taxiways, pilots must comply unless unable.

This is not true. On the ground a pilot can demand a re-route (which is what happened here), and in the air if a pilot does not like a clearance, he can demand a new one or reject the clearance altogether. I have done this many times myself. You just say "negative" and then tell them what you want to do instead. Your idea that pilots "need to follow controller instructions", not sure where you got that from. Are you even a pilot?

@TylerDurden If we had every pilot do as you suggest and wave everything of with a "negative", we would need no ATC at all. Unless unable, you are expected to act according to clearances and instructions.

@Tyler Durden You can demand all you want. I'm happy to say in my career I ran across very few pilots like you. The pilot/controller relationship is a cooperative one. There are many rules that regulate that (as stated in many posts) but in the end, i would hope that we can work together to get the job done. That's what the professionals do. Others can try to convince the FSDO inspector that they have the right to demand what they want (sort of like a two year old).

@SentryRaven I don't know how things are in Europe, but the United States if the pilot doesn't like a taxi instruction and tells ground control to re-route, then they re-re-route.

@Tyler Durden what airport do you fly out of that you tell them you don't like a taxi instruction and they give you another, VATSIM?

@RetiredATC I have never had a reason to change a controller instruction, ground or otherwise. This post isn't about me. However, if I did want to change a taxi instruction, you can be assured I both would have good reason to do so and would expect that demand to be fulfilled by the ground controller.

Neither has authority over the other, they are supposed to work in cooperation.
Negative interactions get reported and can result in unpleasant consequences for either or both.
Legally, at least in the US, PIC is the final authority for the plane and in the event of a disaster after an argument with and following ATC directions, is unlikely to be able to mount a successful defense on the grounds of “just following orders”

It was my experience that the most direct route was understood between the controller and pilot. Consider the ramifications if this were not the case. If another route is needed, it is up to the PIC to inform the controller of that need. Also, if there is ANY question on either side about the instructions or requests, key up the mike and ask! Safe, Orderly, and Expeditious flow of air traffic.

The pilot in command (PIC) always has the final say and decision making power. If a pilot rejects a controller instruction, it is the duty of the controller to react appropriately and make any necessary changes.
Laymen think that controllers are some kind of god-like air cops that are supposed to boss pilots around, but that is incorrect view. First of all, only 3% of airports in the US even have towers at all and many of those only operate during business hours.
Secondly, controllers are not qualified in any way to make decisions about what an aircraft can or can't do because they are not pilots and do not know, nor are they supposed to know the capabilities or safe operating limits of aircraft.
Thirdly, controllers cannot see the actual situation in the air as well as pilots can. I have seen many screwups by controllers because they did not have visibility of the situation or because they interpreted what they were seeing incorrectly.
Controllers perform a valuable function in organizing traffic flow, but in the sky the bosses are the pilots. End of story.

As for the dispute between ground control and the pilot in question from LiveLeak, apparently the pilot thought the taxi route was poorly chosen or not correctly spoken. The article is incorrect in many of its details (you don't land on taxiways obviously!) What apparently happened is that the controller was planning to use Mike for a landing aircraft and directed the Delta pilot to use Lima--a longer route. The pilot probably thought the landing aircraft was far away and that he would be long gone before the other aircraft landed, so he thought the controller was being a jerkoff by making him take the long way around. In a situation like this courtesy dictates following ground control, but the pilot was within his rights to stay on Mike. I doubt the incident was reported, but if it had been the pilot would have been cleared in all likelihood, because all he would have to do is show that the landing aircraft arrived long after he was gone, thereby showing the controller to have had bad judgement. The pilot would only be penalized if his actions could be shown to compromise safety, which is not the case here, since in the worst case scenario the only outcome is that the landing aircraft might have to wait a little longer--not a safety issue.
Just to clarify the "authority" question here with regards to the recording: if you listen you will hear the pilot order "Route on Mike". This basically means he is rejecting the Lima instruction of the controller and ordering him to re-route on Mike. No question who is in charge here.

Your phraseology there is a bit non-standard. Might want to clear up the answer.

@SentryRaven Fix it however you like, I wasn't trying to be exact. Also, my experience is that when "unexpected" things happen, non-standard stuff gets said. Once I had to abort a landing on short final under a similar situation and the controller screamed "TURN LEFT, TURN LEFT RIGHT NOW!!!", not exactly standard phraseology.

Not sure why this answer was down-voted so much

@user Because non-pilots don't like the idea that pilots have authority over controllers. People who don't fly (and a few who do) have the idea that ATC should be some kind of super air cop, bossing the pilots and keeping them safe. They don't really understand how things work in real life (which is that the pilots keep them safe, not the controllers.)

"the pilot would have been cleared in all likelihood, because all he would have to do is show that the landing aircraft arrived long after he was gone" I don't think you know how an enforcement action works.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/3.0/


text:
Am I likely to get permission at a Private Airport?
I'm planning a Labor Day flight to a relative's house, and the nearest airport is a Private Airport that looks to be part of a flying community (multiple houses all with hangars directly off the small runway).
I have no experience with private airports.
If I ask nicely in advance, am I likely to get permission to use it?
Or are they likely to be protective of their privacy and airport?
I realize any answer can't apply in all circumstances, but I'm asking if its worth a phone call and conversation? or if I should just go directly to the nearest public airport?

A "no" you have a "yes" you can get. Give a call and the worst you'll get is a "sorry, I can't help you."

Most of these airport have some sort of organization that sets the rules for use of the airport.  I would contact that organization and ask them for permission.  I have done this several time.  Once or twice I was turned down because of liability issue/concerns since I wanted to stay overnight and they had limited (like one or two) tied down spots available.

Can't hurt to ask!
I don't know the specifics of the situation, but I would be willing to bet that your chances are better than you think.  If it was one farmer with a grass strip and no accommodations for visiting aircraft you might be out of luck, but from what you describe it doesn't sound like one extra airplane on the ground for a few hours is going to make that much of a difference.
In fact, it might be that Fred (or whoever) will also be visiting friends for Labor Day and might be willing to let you use his ramp.
They can't say yes if you don't ask.

Don't forget to inquire about which fuel is available, nothing worse than landing on an unfamiliar airport and being stuck for a few days while you wait for a fuel truck to swing by with some AvGas

Probably yes, if you follow their rules and pay the fee.
From the description you wrote, it appears to be similar to Lakeway Airport. Here is a picture of the runway which has houses next to it and have hangars built.

On their website, they did mention that it is a private airport but if you want to land there, there are some rules and fees which apply.
According to my little knowledge, you should always contact an unfamiliar airport first to get all the necessary information.
Good Luck!

sorry for this being off-topic but I looked at that airport's website and saw it is no more than $50 to land a plane.  Are there really people that own their own planes that balk over $50 to land?

@DeanMacGregor I'm not sure. What I know is that people pay for hangars. Maybe there is some membership for those who have houses. You can call the airport to find out more.

Not all pilots own planes.   Many of us are in time-shares, or clubs where we rent planes by the hour. If I'm only paying $100/hr to rent a plane, then $50 to land is quite a lot.

@DeanMacGregor Imagine hundreds of people dropping in every day, the 50 bucks is probably to deter that. And if they do drop in, 100 times 50 dollars makes a tidy sum towards that new taxiway that'd relieve the need to use the runway for taxiing...

@DeanMacGregor The website says "$50 Landing fee for all twin jets and turbines. $25 for single jets/turbines and helicopters." It says nothing about piston engines, so they might actually let small planes land for free.


text:
What is a weight-shift-control category aircraft?
Aircraft categories include:

Airplane
Rotorcraft
Glider
Lighter than air
Powered lift
Powered parachute
Weight-shift-control

I'm familiar with all of these except for weight-shift-control.  What are they??

Basically, it's a powered hang glider.

Weight-shift control (WSC) aircraft means a powered aircraft with a framed pivoting wing and a fuselage controllable only in pitch and roll by the pilot’s ability to change the aircraft’s center of gravity (CG) with respect to the wing. Flight control of the aircraft depends on the wing’s ability to deform flexibly rather than on the use of control surfaces.

— FAA H-8083-5 Weight Shift Control Aircraft Flying Handbook
They're commonly called "trikes" and are literally big delta-wing hang gliders with a lot more structure and an engine. Check out a cockpit video of one in flight!

And they are superb fun to fly.

But a non-powered hangglider still is cg-controlled, no?

How do they shift the cg? Are there flight controls?

@Lnafziger they shift the CG by moving the entire wing structure. That giant bar the front guy is holding on to moves the wing on a pivot. So you're moving the CG around the center of lift and changing the angle of attack all at the same time.

@StallSpin Cool!  It's really hard to tell that from the small picture.  It looks like part of the frame and he is just holding on!

@yankeekilo yes! ...but they fall outside the FAA's realm, from what I understand.

o.k. - I was thinking phenomenologically, not regulatory :D  The OP does not seem to specify FAA in particular. +1 in any case - do you have an AI prowling the FAA web site for you?

@yankeekilo hah, true. Lnafziger pasted right out of the FAA's list of categories so I didn't even skim for tags!

Well, when I asked "what is it" I didn't think that the regulatory authority mattered (although you correctly determined that it was an FAA category that I was asking about).


text:
The captain of an aircraft flying an international flight is required to have a Restricted Radiotelephone Operator Permit. How do you get one?
47 CFR 87.87 requires the captain of a US registered aircraft to have their Restricted Radiotelephone Operator Permit (RP) unless it is a domestic flight.
How do you go about getting one?  I used the FCC's website a long time ago and remember that it is terribly confusing.  A great answer would include step-by-step directions for those that haven't had to do it yet!

You have to use the remarkably obtuse FCC Universal Licensing System if you want to request a license online. You'll specifically need FCC Form 605, the apparently very-accurately-named "Quick-Form Application for Authorization in the Ship, Aircraft, Amateur, Restricted and Commercial Operator, and General Mobile Radio Services".
From there, you're on your own, I'm afraid. I applied for mine years ago and it looked identical.

Do note that this is essentially a fee on operators who fly internationally, as there's no exam to complete and no proof of eligibility to provide. You simply request the license and pay the application costs. It's a bit silly.

Believe it or not this process was more obtuse before the ULS. They really are trying to make things less terrible. (I won't say they're succeeding, but they are trying...)

It seems silliness tends to persist. I got mine in 1969 but have never been asked to show it.

International law requires licensing of all radio stations and operators.  The FCC has shortcut that within US territory by licensing all US aircraft and pilots "by rule", but if you want to fly outside the US, the FCC needs to issue you a real license like other countries do, and they charge a tiny fee to cover their costs.  The FCC's only blame in this is their hideous web site.